| /* |
| * Copyright 2020 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package androidx.compose.foundation.lazy |
| |
| import androidx.compose.foundation.ExperimentalFoundationApi |
| import androidx.compose.foundation.lazy.layout.LazyLayoutMeasureScope |
| import androidx.compose.ui.layout.Placeable |
| import androidx.compose.ui.unit.Constraints |
| |
| /** |
| * Abstracts away the subcomposition from the measuring logic. |
| */ |
| @OptIn(ExperimentalFoundationApi::class) |
| internal class LazyMeasuredItemProvider @ExperimentalFoundationApi constructor( |
| constraints: Constraints, |
| isVertical: Boolean, |
| private val itemsProvider: LazyListItemsProvider, |
| private val measureScope: LazyLayoutMeasureScope, |
| private val measuredItemFactory: MeasuredItemFactory |
| ) { |
| // the constraints we will measure child with. the main axis is not restricted |
| val childConstraints = Constraints( |
| maxWidth = if (isVertical) constraints.maxWidth else Constraints.Infinity, |
| maxHeight = if (!isVertical) constraints.maxHeight else Constraints.Infinity |
| ) |
| |
| /** |
| * Used to subcompose items of lazy lists. Composed placeables will be measured with the |
| * correct constraints and wrapped into [LazyMeasuredItem]. |
| */ |
| fun getAndMeasure(index: DataIndex): LazyMeasuredItem { |
| val key = itemsProvider.getKey(index.value) |
| val placeables = measureScope.measure(index.value, childConstraints) |
| return measuredItemFactory.createItem(index, key, placeables) |
| } |
| |
| /** |
| * Contains the mapping between the key and the index. It could contain not all the items of |
| * the list as an optimization. |
| **/ |
| val keyToIndexMap: Map<Any, Int> get() = itemsProvider.keyToIndexMap |
| } |
| |
| // This interface allows to avoid autoboxing on index param |
| internal fun interface MeasuredItemFactory { |
| fun createItem( |
| index: DataIndex, |
| key: Any, |
| placeables: Array<Placeable> |
| ): LazyMeasuredItem |
| } |